Plans for a ressurected rotary engine appear to have hit a snag with Mazda CEO Masa-michi Kogai claiming that the required volumes for commercial viability are unrealistic.

Speaking to Automotive News, Kogai said that a new rotary engine would need to hit volumes of 100,000 annual units, a figure considered unrealistic

“No plans now,” Kogai said in an interview Friday. “It has to be a viable commercial proposition. If we are going to adopt it, it has to be a product that can generate at least sales of 100,000 units a year. We have to be able to achieve a profit.”

However, Kogai said that research on the rotary engine will continue, specifically with regards to alternative fuels. The rotary engine has so far been able to run on hydrogen and even kerosene in additional to gasoline, and Mazda doesn’t appear to be discontinuing rotary R&D any time soon. However, Kogai’s mission is focused around improving profitability, and increasing efficiencies is his first priority.

Wouldn’t a rotary engine be ideal for the ICE component of serial hybrid drivetrains? They’re small and lightweight, and the lack of low-end torque probably wouldn’t be as problematic, since they’d be running at more-or-less constant higher RPMs.

Way less efficient, and inevitably so. I wrote about them in ’04, and had they had any potential for better fuel economy, I would have gladly bought an RX-8. But just one problem is that from the point of view of combustion efficiency, the ideal combustion chamber would be as close as possible to spherical, to minimize heat loss. But the rotary combustion chamber is almost two dimensional–flat–the worst possible shape.

I had an RX-8 for a week while I was writing the article. It was wonderful to drive. But 22 mpg even under good conditions–not nearly as good as a Corvette.

I am no expert on internal combustion, and have never even driven a rotary, but this feels like a decision that was 30+ years overdue. Lousy fuel economy, lack of scale within the industry, reliability issues with rotor tips and lack of interest from mainstream consumers were more than sufficient to scare away every other automaker long ago.

I am glad Mazda still exists and know that they need to be thoughtful about how they spend their scarce development funds. Moving on from the Wankel just means they can focus on more mainstream technologies that will reinforce their core models and allow them to stay alive. All good.

I am considering an FRS/BRZ. I just lament the dull sound. The boxer actually can sound interesting with unequal length headers, but it’s still not like a good six or eight. The S2K does not sound good to me, much as I respect the motor.

As far as the rotary not winning races, I have to contest that. The rotary was so dominant that it was banned. More recently, Mazda had plenty of success with their RX8 running a 20B.

At the time Mazda released a rotary-engine powered car to market (1972), its fuel economy compared favorably enough with its contemporaries and fuel economy was not a priority. By contrast, using a thermal reactor and running the engine a bit rich provided an easy way of meeting emission standards of the time with better driveability. For its size and weight, the rotary was quite powerful; and it was much smoother than the 4 cylinders of lesser output, which lacked balance shafts. Finally, with a redline of 7,000 rpm — with power usable right up to and beyond that speed — the rotary engine was leagues above reciprocating engines, most of which had a 5,000 rpm redline with usable power only up to 4,000.

Assuming the car was not allowed to overheat and was properly oiled, the apex seals lasted as long as piston rings in most reciprocating engines of the time.

So, it’s hard to see how introducing the rotary was a mistake. The problem — probably unknown at the time — was that its development potential was not as great as the reciprocating engine. The rotary is not thermally efficient, with a relatively large combustion chamber surface area for its volume. And, there’s no easy way of varying the timing or duration of valve opening as is now commonplace on reciprocating engines.

So, the Mazda folks mad the right call. And yes, I owned one of the first Mazda rotaries (RX-2) for 5 years. It was stone reliable but needed new seals by the time I sold it. . . and was thirsty.

“Finally, with a redline of 7,000 rpm — with power usable right up to and beyond that speed — the rotary engine was leagues above reciprocating engines, most of which had a 5,000 rpm redline with usable power only up to 4,000.”

I’m not sure I understand why some people believe redline is of any importance other than for internet bragging.

Because power in horsepower at a given RPM is equal to torque in foot pounds at that RPM multiplied by that RPM divided by 5252.

Or, more succinctly:

P(r) = (T(r) * r) / 5252
where P is power in horsepower
T is torque in foot pounds
r is engine speed in RPM.

So for a given size of engine producing a given amount of torque, the faster an engine can spin the more power it can produce. For example, my Acura RSX Type-S produces all of 140 ft-lbs of torque. If it were limited to the usual 6,500 RPM redline it would only make about 170hp. Instead it spins clear up to 8,000 RPM and makes 200hp.

Power in a piston engine is equal to PLAN. P is pressure, L is length (aka length), A is area (aka bore), and N is booms per period of time (aka RPM). To make more power you must increase one of those 4. A bigger engine yields more L and A. A faster engine yields more N. A turbocharger, supercharger, better cams, better intake, better exhaust yields a better P. In the case of forced induction a MUCH better P.

Remember that N is inversely proportional to L. As N increases L must decrease or vice versa (neglecting improvement in material quality of the crankshaft/conrod/etc). My personal preference for power is a high N, sacrifice L, and have a larger engine through A alone. P is nice but I haven’t gone down the turbocharging route (yet). A good example of the sort of engine that I love is the 4.2L Audi V8 in the Audi RS4 and R8. The stroke is only 84.5mm but the bore is 92.8mm. The torque is a “mere” 317lb-ft but the horsepower is a high 420hp at 7,800 RPM.

I admit that it’s a far more expensive way to get power than the simple method of “put in something bigger”, but I feel that it’s just the right way to do things.

#2 you seem to boil it down to personal preference. Like I said, internet bragging.

“So for a given size of engine producing a given amount of torque, the faster an engine can spin the more power it can produce. For example, my Acura RSX Type-S produces all of 140 ft-lbs of torque. If it were limited to the usual 6,500 RPM redline it would only make about 170hp. Instead it spins clear up to 8,000 RPM and makes 200hp.”

so what? another engine can make the same 200 hp at a lower rpm and have better around town drivability. Cars have these things called “gears.” I don’t care if your wundermotor revs to 8k rpm if I practically never run it there.

I was asking why a higher redline is somehow “important.” I was NOT asking why you like it more.

He answered you. The ability to rev allowed the rotary to achieve relatively high output per liter from a light engine that didn’t take up much space, good attributes for a small sports car at the time. Not particularly competitive by today’s standards, but it was then.

Yes, it is personal preference. But it is not just for “internet bragging”. I simply find just using a larger engine to be a lazy and cheap solution. A higher revving engine will simply be less responsive (longer stroke and wider heavier pistons) to wind up, and generally have a better power to weight ratio.

“so what? another engine can make the same 200 hp at a lower rpm and have better around town drivability. Cars have these things called “gears.” I don’t care if your wundermotor revs to 8k rpm if I practically never run it there.”

Well, I do wind it up to at least 7,500 RPM no less than 3 times every drive, and above 6,500 more times than I can count. Plus, my car has wonderful in town drivability. If I want to accelerate to pass or merge into traffic, I just downshift to 1st or 2nd gear if I am in town and 3rd or 4th gear if I am on the highway. If I want to cruise I just run in 5th or 6th for city and 6th for highway.

Honestly, if my car had a larger engine I probably would have passed on it and kept looking for something else. Like a new FR-S or a used RX-8 or an Infiniti G37 coupe.

In fact, my recollection from ’04, when I wrote about the rotary, is that the motive part of the engine–the part that’s generating the torque–is turning at only about half the claimed RPM. It’s the crank–which is doing nothing but tranfering the torque to the transmission–that’s turning at the rated RPM.

I remember driving the economy-aimed R100 coupe around 1970, and being uphappy with fuel economy compared to my 510 and Capri. My view is Mazda has spent the most engineering and real world time perfecting the rotary, and if they can’t design it to be more practical, no one can. I’m also worried that the niche Mazda customer, including Mazda3 and Miata fans like me, don’t want a rotary engine anywhere near their products. Mazda has so far made some very good choices when it comes to their cars, and the rotary engine just wastes good engineering money after bad, and Mazda can’t afford that these days, and I want Mazda to stay in the product mix for me and my friends.

Uh, has he ever used the internet before? If he had, he’d know darn well that there’s a very successful business case to be made for a diesel rotary Miata wagon with a manual transmission. The entire internet would buy one right now.

I believe the 220 pound weight for the Miata engine may be high since the 2nd source lists “shipping weight”, and therefore includes packaging and possibly some engine accessories not included on the RX-8 engine when it was weighed.

It would be interesting to see the impact of an alumnimum block, but even if it cut the weight 25% that would only add up to 53 pounds.

If you think the three generations of RX7 were not compelling cars, I don’t know what to say. The RX8 is still a faster car than the BRZ/FRS, and it has rear doors.

On a reliability basis there have been issues at certain times, but plenty of folks have loved cars with reliability problems: Jags, old Alfas, all Ferraris ever, etc. And original RX7s are known to go over 200K miles in a racing environment when treated well.

The gen-1 RX-7 was compelling 30-some years ago, and sales reflected that. But soon word got out about the multitude of real-life ownership issues, which also included rust. At a time when engines were adopting EFI and becoming more reliable, the Wankel seemed stuck in the bad old days that nobody wants to revisit.

The Wikipedia entry for the RX-7 reads like a puff piece penned by an enthusiast, with NO mention of “seals” or “reliability”, two keywords that inevitably arise in discussions of Mazda’s rotary-powered cars. The entry for the rotary engine itself is more even-handed, however.

First you said never, now you say 30 years. I still say it’s more recent.

The FD is still known as one of the greatest driver’s cars of the decade. It was light, so it had its issues, but lightweight low volume cars always have (see Lotus).

And every Japanese car of that era (most cars period) had rust issue in the snow belt. But I had a CA 85 GSL in the 90’s that was pristine.

Ultimately enthusiasts cars are almost always a tradeoff. If you want an appliance, buy a Toyota.

To me, it is worth a bit of sacrifice to have an enthusiast option with a high output small displacement motor that loved to be driven hard. I realize that I am in the minority, but that doesn’t make the cars any less joyful. The world is a better place for the Lotuses, Caterhams, and RX7s that were bought by the few who appreciated them. If practicality were the most important thing in the world, it would be a dull world indeed.

I can’t speak to the engine in the new Miata, but rotaries are a hobby of mine. The weight Renesis is hard to pin down, but it’s about 270lbs to 300lbs fully dressed (what is “fully dressed” is the source of the vagueness of rotary weight).

The actual block and flywheel without accessories, intake manifold, exhaust manifold, or turbos weighs about 155lbs. This figure for the bare block hasn’t actually changed much for the entire production run of the 13B from 1985 until 2011. The real weight is found in the rest of the engine equipment. For example the twin turbo in the third gen weighed around 390lbs.

The big problem for weight with early rotaries was that giant cast iron lump that they called an exhaust manifold or “thermal reactor”. Switching to a good set from Racing Beat can really drop the weight of an older rotary.

So, in regards to my assertion that the rotary is an aircraft engine at heart. I will only touch on one reason that I think the rotary engine is a plane engine.

First is the obvious problem of tip sealing. One of the problems of the rotary is that the tip seals have a tough time sealing gasses from one chamber to the next. The seals are pressed into the housing surface by a set of 2 springs resting between each seal and the rotor. There is something though that will work better to press the seal into the rotor housing than any spring. Centrifugal force. As the rotors spin faster, the seals are rammed into the rotor housing far more firmly than the springs could ever do. The faster the rotor spins the better the engine seals. Now consider a car, even a race car. It is constantly dropping to very low RPMs as the car brakes. Airplanes on the other hand will let an ICE engine drone at the same relatively high RPM for hours on end.

To that end, here is a company developing an FAA certified aviation rotary engine.
http://www.mistral-engines.com/

And a US Army UAV using a rotary engine.
http://en.wikipedia.org/wiki/AAI_RQ-7_Shadow

I mourn the loss of the rotary in auto use, and I dread not finding parts for my RX in the future. But I genuinely think that auto use was not the right use of a rotary, and I think it might have a brighter future in aviation use.

Excellent point about use in aviation. The RE is very common in that due to light weight for power delivered, compact size, and high reliability in in NA form.

At the Deals Gap Rotary Rally a few years ago to one of the race shops that now had a good business going with aviation engines. I forget the exact details but he was building all aluminum 3 rotor engines with were coming in under 300 lbs ready to install as I recall.

The required MPG due to CAFE, and displacement in the EU and China makes this impractical. A niche creation for a niche sports car doesn’t make much sense. Finally, Mazda had solid experience with forced induction.

Kind of sad news, but it’s a good business decision. As-is the rotary has been a niche engine, and a business case for it would require broad availability. If they could R&D the thing into a V6 replacement, maybe. In fact, since they have no V6 plans, that’s probably not the worst idea.

Anyway, right now SkyActiv is selling like hotcakes, and so is Kodo. Taking their eye off the ball would be a bad move, so it’s smart of them to move rotary research off to the background for now. Grow the business and be profitable for a while.

Many comments here agreeing this is a sound business decision, and I too see it that way. Mazda is still a small company volume wise, so to me it makes sense to focus on whats really working for them to grow and become stronger before focusing on something like a next gen rotary.

There’s a way to make this engine reach the sales he wants: make it an optional engine for Every Single Model Mazda Sells! Don’t just drop it into a single ‘benchmark’ model. I mean sure, the RX series was great, but too limited. My pizza delivery guy took a Miata and stuck a rotary in it and absolutely loves it! He says he gets better gas mileage than it ever did on the original 4-banger.

I have an RX-8, but I often think of swapping the engine for something with more power & torque. And if I did that, I’d also love to take the rotary and drop it in a Miata where it’s deficiencies won’t be so noticeable.

And of course, I’d have to get custom badging for an “MX-8″ and an “RX-5.”

Here is something I always wondered about with regard to rotary engines:

1) Felix Wankel was a German engineer;
2) He patented his invention in Germany;
3) German car companies (7 then) have a history of innovation and desire to explores new technologies;
4) Not a single German car company commercialized the Wankel engine in any of their vehicles.

Why?
Did they figure out rotary-engine issues, for the long term, that we just didn’t understand in 1970?

Thanks for the correction. It appears then that both Mercedes and NSU did “dabble” with rotaries for at least a little while. It may be that “couldn’t figure out” was less of the issue, and that “limited long-term future” was more of the issue.

First, I believe the reasoning for this decision is sound and wise. But the 100k/yr threshold is bit high, IMO. At this point, the rotary is an indulgence, and Mazda can’t afford that right now. Thus, I cannot criticize the decision.

That being said, I hope Mazda gets on sound-enough financial footing that they can afford the luxury to sell another RX car, and short of that, sell the 16X as crate motor. After all, eating healthy is good, but having some dessert now and then is a good thing.

Thinking of the rotary’s weaknesses, I have to wonder how much improvement it would have seen if all the car companies made them. Similarly, how little improvement in the piston engine would there have been if only one company had worked on it? FWIW, as long as I’ve known about the rotary, it’s always been a step behind piston engines. I do believe there is room to make it better in efficiency, emissions, etc. But when that is done, the same improvements will be had from pistons. I don’t see a way it will ever leapfrog the piston engine.

I know others have joked about this, but I actually wonder if the particulate filters used on diesels and their tendency to increase oil levels could actually help the rotary. Since one of its problems is unburned hydrocarbons like diesels, the filter should improve emissions directly. If the system suffers the same problem of the fuel ending up in the oil, and since oil is injected into the engine (and burned) anyway to lubricate the apex seals, contamination may not matter too much. And rising oil levels would actually be maintaining oil levels. Owners already have to check/change oil frequently, so that’s not an added expense.